Sterile medical liquid, such as parenteral solution, is commonly infused into a patient's vein from a container hanging above the patient. The sterile liquid flows by gravity through a tubular administration set connected at one end to the container and at an opposite end to a venous needle in the patient.
These sterile parenteral solutions, such as 5% dextrose, normal saline, etc. are frequently supplied to the hospital in sterilized containers. When these bottles are of the rigid glass type, a vacuum within the bottle can be used to test the hermetic seal at the bottle closure. One such testing device is a thin, latex disk fitting over an opening in a rubber stopper of an evacuated glass bottle. As long as the bottle holds the vacuum, the disk will show a visual deformation into the stopper opening. A leak in the bottle causes a vacuum loss and the latex disk resumes its undeformed shape.
Recently, thermoplastic bags and bottles have been proposed for intravenous solutions because of improved handling characteristics, reduced freight costs, easier disposal, etc. Such thermoplastic containers are not sufficiently rigid to continuously maintain a vacuum. Thus, a permanent vacuum within the bottle cannot be used as a leak test.
In parenteral solution bottles, it has also been proposed to provide an evacuated chamber between two metal caps fitted to a neck of a bottle. The vacuum within the chamber holds a top of an outer cap in a depressed state. If the vacuum is lost, the top of the outer cap will deflect outwardly indicating a leak. Such a preformed, 3-dimensional cap structure is expensive to manufacture. It is also difficult to precisely control the springiness of the top wall of the outer cap so that it will work properly.